Verde Valley American Viticultural Area

Almost all of the Verde Valley AVA has a Growing Season Temperature¹ between 70°F and 75°F (21°C and 24°C), based on data² from 1981 through 2010.

Growing Season Temperature is the average temperature between April 1 and October 31. It is a common climate-viticulture classification used to compare winegrape-growing regions and to gauge which varieties might do well in an area. Different varieties require different amounts of heat accumulation during the growing season to ripen fruit.

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¹ Jones GV and colleagues (2005)
² TopoWx ("Topography Weather")

Much of the Verde Valley AVA has Winkler Index³ values between 2222 and 2700, based on data² from 1981 through 2010. Isolated areas in the northern and southern parts have long-term normal values greater than 2700.

Winkler Index values are cumulative growing degree days (10°C-based) between April 1 and October 31. It is a common climate-viticulture classification used to compare winegrape-growing regions and to gauge which varieties might do well in an area. Different varieties require different amounts of heat accumulation during the growing season to ripen fruit.

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² TopoWx ("Topography Weather")
³ Winkler AJ and colleagues (1974)

Almost all of the Verde Valley AVA has Huglin Index⁴ values greater than 3000, based on data² from 1981 through 2010. An area in the northwestern part has long-term normal values that are lower and between 2700 and 3000.

Huglin Index values are cumulative growing degree days (10°C-based) between April 1 and September 30 that additionally account for maximum temperature and daylength. It is a common climate-viticulture classification used to compare winegrape-growing regions and to gauge which varieties might do well in an area. Different varieties require different amounts of heat accumulation during the growing season to ripen fruit.

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² TopoWx ("Topography Weather")
⁴ Huglin P (1978) Nouveau mode d’évaluation des possibilités héliothermiques d’un milieu viticole. Comptes Rendus de l’Académie d’Agriculture de France, 64, 1117-1126

Almost all of the Verde Valley AVA has values of Biologically Effective Degree Days⁵ between 1600 and 1800, based on data² from 1981 through 2010.

Values of Biologically Effective Degree Days are cumulative growing degree days (10°C-based) between April 1 and October 31 that additionally account for how vine growth rate differs at different temperatures, daylength, and diurnal temperature range. It is a common climate-viticulture classification used to compare winegrape-growing regions and to gauge which varieties might do well in an area. Different varieties require different amounts of heat accumulation during the growing season to ripen fruit.

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² TopoWx ("Topography Weather")
⁵ Gladstones J (1992)

Much of the central and southeastern parts of the Verde Valley AVA has an average date of the last spring freeze during the first half of April, based on data² from 1981 through 2010. Many western and northern areas along the proposed Verde Valley AVA boundary have dates during the second half of March.

The last spring freeze is the latest occurrence of daily minimum temperature below 32°F (0°C) from January 1 through July 31. Freezing temperatures close to the start of the growing season can damage vines and reduce yield.

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² TopoWx ("Topography Weather")

Almost all of the Verde Valley AVA has an average date of the first fall freeze during the first half of November, based on data² from 1981 through 2010. Some western and northern areas along the proposed Verde Valley AVA boundary have dates during the second half of November.

The first fall freeze is the earliest occurrence of daily minimum temperature below 32°F (0°C) from August 1 through December 31. Freezing temperatures close to the end of the growing season can damage vines and unharvested fruit, as well as curtail post-harvest photosynthesis and carbohydrate accumulation.

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² TopoWx ("Topography Weather")

Limestone is a known parent material occurring in the central part of the Verde Valley AVA, east of the Verde River.¹ Limestone and sandstone, limestone and shale, sandstone, and basalt appear in adjacent areas. Granite and igneous rock are present in locations along the valley floor.

Parent material is the type of bedrock from which soil forms. As a component of vineyard soils, it influences water infiltration, storage, and drainage, erodibility, pH, nutrient availability, and heat absorption, which affect root, canopy, and fruit growth.

¹ Gridded Soil Survey Geographic (gSSURGO) Database for Arizona, United States Department of Agriculture, Natural Resources Conservation Service, July 2020 Release. Not all areas have complete or available data.

Gravel and sand are the most abundant rock types in the Verde Valley AVA for many areas along the valley floor and to the west of the Verde River.² Conglomerate and sandstone also occur in several areas to the west of the Verde River, as well as to its east. Basalt and alkaline basalt are present in areas along the northeastern and northwestern boundaries. Sandstone and siltstone also are present in the northwestern part of the AVA.

Major rock types are the most common solid, loose, and unstratified rocks, defined by composition, texture, and origin. As a component of vineyard soils, they influence water infiltration, storage, and drainage, erodibility, pH, nutrient availability, and heat absorption, which affect root, canopy, and fruit growth.

² US Geological Survey Mineral Resources, Arizona geologic map data

Known depths to bedrock are less than 12 inches for much of the east-central part of the Verde Valley AVA, although depths between 24 and 36 inches and between 36 and 48 inches occur in some adjacent areas.¹ Depths less than 12 inches and between 12 and 24 inches exist in the northwestern part.

Depth to bedrock represents the distance from the soil surface to the top of a restrictive layer, such as bedrock and other dense layers. As a component of vineyard soils, such restrictive layers can impede water drainage and restrict root depth.

¹ Gridded Soil Survey Geographic (gSSURGO) Database for Arizona, United States Department of Agriculture, Natural Resources Conservation Service, July 2020 Release. Not all areas have complete or available data.

Fine sandy loam, loam, sandy clay loam, sandy loam, silty clay loam, silt loam, and very fine sandy loam are known to occur in areas throughout the Verde Valley AVA.¹ Sand is common along surface water features like the Verde River and Oak Creek. Areas of loamy fine sand exist in eastern and northeastern parts of the AVA.

Texture represents the relative proportions of mineral grains in soil based on their size. As a component of vineyard soils, it influences water infiltration, storage, and drainage, erodibility, pH, nutrient availability, and heat absorption, which affect root, canopy, and fruit growth.

¹ Gridded Soil Survey Geographic (gSSURGO) Database for Arizona, United States Department of Agriculture, Natural Resources Conservation Service, July 2020 Release. Not all areas have complete or available data.

Much of Verde Valley AVA has well-drained soils.¹ Excessively and somewhat excessively drained soils are common along surface water features like the Verde River and Oak Creek. An area of somewhat excessively drained soil also exists in the north-central part of the AVA.

Drainage class refers to the rate at which water drains from soil, how frequently water occurs in soil, and at which soil layers water is found. As characteristics of vineyard soils, these conditions influence soil moisture and nutrient and oxygen availability, which affect root, canopy, and fruit growth.

¹ Gridded Soil Survey Geographic (gSSURGO) Database for Arizona, United States Department of Agriculture, Natural Resources Conservation Service, July 2020 Release. Not all areas have complete or available data.

Several areas in the northern half of the Verde Valley AVA have available water storage in the top approximately 40 inches of soil between two and five inches.¹ Several areas along the northwestern and eastern boundaries of the AVA, as well as along surface water features like the Verde River and Oak Creek, have values less than two inches. Values between one and six inches are typical for much of the southern half of the AVA adjacent to the Verde River.

Available water storage represents the amount of water soil can store, in this case in the top approximately 40 inches (1 meter), for plants. As a characteristic of vineyard soils, it influences how much rain, melted snow, and irrigation can be absorbed as well as irrigation frequency.

¹ Gridded Soil Survey Geographic (gSSURGO) Database for Arizona, United States Department of Agriculture, Natural Resources Conservation Service, July 2020 Release. Not all areas have complete or available data.

Soil pH between 8 and 9 is known to occur for much of the Verde Valley AVA east of the Verde River, as well as in the northwestern part of the AVA.¹ Soil pH between 7 and 8 exists in areas near surface water features like the Verde River and Oak Creek, in addition to the northwestern part of the AVA.

Soil pH reflects the relative acidity (values less than 7) or alkalinity (values greater than 7) of soil. As a component of vineyard soils, it influences nutrient availability, which affects root, canopy, and fruit growth.

¹ Gridded Soil Survey Geographic (gSSURGO) Database for Arizona, United States Department of Agriculture, Natural Resources Conservation Service, July 2020 Release. Not all areas have complete or available data.

Much of the Verde Valley AVA has elevations between 3,000 and 4,000 feet (914 and 1,219 meters).^1,2 An area in the far northwest has elevations between 4,000 and 5,000 feet (1,219 and 1,524 meters). Higher elevations, some of which exceed 7,000 feet (2,134 meters), occur just outside of the western boundary.

Elevation creates pronounced differences in temperature and precipitation. Average temperatures at higher elevations are cooler than those at lower ones. Average precipitation amounts at higher elevations are greater than those at lower ones.

¹ US Geological Survey, 1 arc-second (approximately 30 meters) digital elevation model
² relative to the North American Vertical Datum of 1988 (NAVD 88)

The northern and southern parts of the Verde Valley AVA mostly have slopes less than 5%.¹ Slopes in the central part often are between 5% and 30%. Slopes in the far northwestern part are commonly greater than 30%.

Slope represents the change in elevation across an area. It can influence the amount of sunlight directly reaching vines and thus temperatures within a vineyard, as well as cold-air drainage, water infiltration, soil erosion, and use of vineyard equipment.

¹ US Geological Survey, 1 arc-second (approximately 30 meters) digital elevation model

Many areas along the western boundary of the Verde Valley AVA face north or east.¹ Much of the rest of the area faces south or west.  

Aspect is the cardinal direction that a slope faces. Like slope, it can modulate sunlight that directly reaches vines and thus temperatures within a vineyard. Locations with south- and west-facing slopes experience higher values of these environmental conditions.

¹ US Geological Survey, 1 arc-second (approximately 30 meters) digital elevation model

The Verde Valley AVA is centered on the confluence of Oak Creek, which flows from the northeast, and the Verde River, which flows along the valley floor from northwest to southeast.³ Several other creeks, washes, and ephemeral streams drain into and through the area.  

Natural features that are perennial, intermittent, or ephemeral and engineered features like canals, ditches, and reservoirs make up surface water. In addition to directing water across a landscape, these features can channel cooler air from higher elevations to lower ones on nights with little to no wind, influencing spring and fall freeze risk as well as diurnal temperature range during summer.

³ US Geological Survey, National Hydrography Dataset